gfs2: move gfs2_xattr_handlers_max to .rodata

This makes it harder for accidental or malicious changes to
gfs2_xattr_handlers_max at runtime.

Cc: Bob Peterson <rpeterso@redhat.com>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: cluster-devel@redhat.com
Signed-off-by: Wedson Almeida Filho <walmeida@microsoft.com>
Link: https://lore.kernel.org/r/20230930050033.41174-13-wedsonaf@gmail.com


Signed-off-by: Christian Brauner <brauner@kernel.org>